The present invention relates to a system for optimally controlling patient temperature during a surgical procedure, and more specifically to a temperature control system which employs a plurality of heat exchange devices controlled by a central controller.
Cardiovascular surgery though safe and effective has inherent risk associated with the artificial oxygenation and pumping of the patient""s blood over extended periods of time. Some primary sources of morbidity is micro air, particulates and activated blood components that may lodge in the vasculature causing diffuse ischemic sites. One way to minimize organ damage during such a procedure is through the inducement of hypothermia. Hypothermia has been shown to bestow protection to the heart, brain, kidneys, liver and spine.
Hypothermia during a cardiovascular procedure may be induced by cooling blood in the bypass circuit. Temperature control has been provided through use of a device such as a blood oxygenator, which includes a blood/water heat exchanger. In such a system, blood temperature is controlled by controlling water temperature on the opposite side of the water/blood heat exchanger in the circuit. The perfusionist running the equipment determines the correct water setting and duration of temperature changes in order to achieve a desired patient core temperature.
Upon completion of a cardiovascular procedure, hypothermia must be reversed as quickly as possible. This typically must be done prior to the patient awaking from anesthesia to prevent detrimental affects of hypothermia. Mild hypothermia in the medical or the surgical patient has been thought to prolong the time to extubation, contribute to coagulopathies, increase the chance of infection, and increase cardiac demand as a result of shivering.
As part of the surgical procedure, a typical method for rapid re-warming at the end of the case is to heat the blood in the heart/lung circuit. In order to achieve a normothermic core temperature, while minimizing the time on bypass, the blood temperature is often raised to hyperthermic levels. Research has indicated that maintaining a small differential between arterial blood temperature and brain temperature provides for an optimal therapy. This would typically require feedback control from a sensor close to the brain, or controlling the rate of blood temperature rise to minimize the difference. Further, even when the core temperature is raised to normothermic temperatures with the bypass circuit, without extending the time at temperature, an afterdrop occurs postoperatively due to re-distribution of cold peripheral blood into the core.
The inventors have recognized that to provide optimal patient temperature control during a surgical procedure a plurality of temperature control systems, each in communication with a central controller, may be employed. Further, the inventors have recognized that a system which provides temperature control of the blood in a bypass circuit in addition to temperature control of the periphery of the patient""s body may achieve the benefits of optimal temperature control during the inducement of hypothermia as well as minimizing any potential detrimental affects during patient re-warm.
Described herein is a patient""s temperature control system which employs a plurality of heat exchange devices. Each heat exchange device is configured to affect temperature in one or more patient regions. For example, heat exchange devices may comprise a set of temperature control pads which provide heating and cooling to the periphery of a patient, as well as a blood/water heat exchanger which provides temperature control for patient blood while on bypass. Further, the system includes at least one controller configured to receive measured temperature signals from a plurality of temperature sensors, said controller further configured to generate and transmit control signals to each of the plurality of heat exchange devices so as to affect one or more measured patient temperatures. The plurality of heat exchange devices is each further configured to receive the control signals and perform the heat exchange to the designated region according to the received control signal.
In one configuration of the invention, the measured patient temperatures may comprise the core body temperature, patient blood temperature, as well as a temperature for the heat exchange medium (e.g., water) employed in the heat exchange device. The core body temperature may be measured in such locations as the nasopharynegeal region, the bladder, and/or the rectal region.
The controller described herein may be further configured to include, store and employ target temperatures to be met and maintained by the heat exchange devices during one or more modes of operation. These modes of operation may correspond to portions of a surgical procedure. For example, during a cardiovascular procedure different target temperatures may be established prior to intubation, after intubation, while on bypass, prior to extubation, and finally post-operatively.
In one configuration of the invention, each of the plurality of patient heat exchange devices may be part of a stand-alone temperature control system, each of which includes a controller configured to control a particular heat exchange device independent of any other temperature control systems. According to the invention described herein, each of the temperature control systems patient heat exchange devices may be further configured to be connectable to at least one other temperature control system so that both systems may operate under centralized control. In yet another configuration of the invention, the relationship between the controllers of each system may be that of a master/slave. The connection between the systems may be established through use of a communication protocol such as RS-232 through a port in a housing for each of the temperature control systems. The connection may be a direct electrical connection using a cable or other devices such as wireless communication connections may be employed.
As mentioned above, the controller may be configured as part of a temperature control system which is connectable to one or more heat exchange devices. In one configuration of the invention, the temperature control system may comprise one or more reservoirs for storing and circulating water through the one or more heat exchange devices, such as control pads which are positionable on a the periphery of a patient and/or a blood/water heat exchanger and oxygenator. The controller may be further configured to employ one or more predictive algorithms for controlling water temperature.
The system described herein may further include at least one interactive display through which patient temperature information may be presented and various modes of operation initiated. Specifically, the interactive display may include one or more display screens which present information such as temperatures being monitored at different locations. These temperatures may include core body temperature, patient blood temperature, as well as water temperatures within the temperature control systems. Further, the display may include various input devices so that a system user may scroll through various items of operational information such as modes of operation stored in memory, and select a desired mode. Prior to operation, various programming such as instructions for simultaneous control of multiple heat exchange devices as well as target temperature during various modes of operation may be entered through the interactive display.
In the configuration of the invention, where one or more temperature control systems are connected in a master/slave relationship, a controller of a designated temperature control system may be identified as a master (central) controller. The central controller may be provided with programming for controlling one or more slave temperature control systems. Further, the display in the master temperature control system(s) may be configured to present temperature and other operational information received by the temperature control system connected as slave(s). Once the data link for master and slave controllers are disconnected, the stand-alone temperature control systems may then operate independently.
Prior to beginning a surgical procedure, heat exchange devices to be used are positioned so as to provide heat exchange to a patient in a desired region. For example, temperature control pads are positioned on the periphery of the patient and connected to the temperature control system. Further, a core body temperature sensor is connectable to one of the temperature control systems, which in one configuration of the invention may be the temperature control system for the temperature control pads. Blood temperature may be controlled through a blood/water heat exchanger and oxygenator which circulates the blood of the patient while on bypass. During a surgical procedure, a master controller may receive temperature signals from a plurality of temperatures sensors configured for measuring selected patient and system temperatures. Prior to the initiation of the surgical procedure, certain target temperatures are identified as well as modes of operation are identified which are stored in memory. This information may be entered through the interactive user interface.
During a surgical procedure, one or more modes of operation may be employed for providing optimal patient temperature control. Through use of the interactive display incorporated in the master temperature control system, a particular mode of operation may be identified and selected. Once the surgical procedure has begun, the mode of operation may be initiated by a system operator (e.g. perfusionist). For example, during a surgical procedure which requires a patient to go on bypass, different modes of operation may be established prior to intubation, before cannulation, while the patient is on bypass, re-warm prior to extubation, and postoperatively.
For example, in the configuration of the system described herein where the heating devices comprise a blood/water heat exchanger and temperature control pads, during the initial phase after intubation (prior to going on bypass) the temperature control pads are employable for lowering the core body temperature of the patient to a desired level. Once this core body temperature is achieved cannulation and initiation of heart-lung bypass may be performed. While on bypass, a core body temperature may be maintained through monitoring and use of the blood/water heat exchanger. Moderate rewarming of the periphery of the patient may be had through control of the temperature control pads. The core body temperature is controlled through adjustment of water temperature according to a predictive algorithm.
Upon completion of the surgical procedure, a patient re-warm may be performed through raising of the pad temperatures. During the re-warm the core body temperature can be accurately controlled using the blood/water heat exchanger. Once off bypass the control pads are used to control temperature exclusively and the data link between the temperature control systems may be terminated.